The invention relates to a filter insert, configured as a pleated pack and made of thermoplastically bondable nonwoven material, such as fiber material, and a method of its manufacture.
Such a filter pack and method are known from EP 0 438 639 B1, corresponding to U.S. Pat. No. 5,167,740, which is incorporated herein by reference.
In particular, the invention, like that disclosed in U.S. Pat. No. 5,167,740, relates to a filter insert comprising a planar filter medium folded and then set in its folded (pleated) form at a specific fold spacing.
In U.S. Pat. No. 5,167,740, after the process step of creating a defined fold spacing, the two outer edges of the filter insert are clamped into comb-like profiles, having profiles substantially corresponding to the fold pattern to engage in toothed fashion into the top and bottom of the folds. The spacing between the comb-like profiles is chosen to be the same as or slightly less than the thickness of the nonwoven material.
In U.S. Pat. No. 5,167,740, the filter material is allowed to project beyond the comb-like profiles, on each long side of the folded pack, a distance equal to 1.5 to 2.5 times the fold spacing. Subsequently, the resulting excess-length material is folded by means of a pressure element acting laterally thereon, until the excess-length material lies against the adjacent fold end so that the edges overlap. The overlap zone is simultaneously thermally bonded by means of energy delivered via the pressure element.
A filter insert produced in this manner possesses great inherent stability, so that an additional receiving frame can be omitted for installation in a filter housing. A further advantage of the filter insert manufactured with this known method is its good recycling capability, since the filter insert is made of only one material, namely the nonwoven material. The known filter insert is flexurally strong in three coordinate axes, the flexural strength resulting from bonding of the excess-length material of each fold to the adjacent folds. The consolidated side surfaces thus perform the function of a frame. Because of the large excess length, which equals 1.5 to 2.5 times the fold spacing, creasing and overlapping of all adjacent folds in one direction results in a closed side surface which imparts three-dimensional rigidity to the known filter.